1. Field of the Invention
The present invention relates in general to trolley-assisted vehicles, such as dump trucks, used for the transportation of ores in large mines. In an area in which low cost electric supply is available and thus the fuel cost is comparatively high, trolley-assisted dump trucks are conveniently used nowadays for decreasing the transportation cost. Furthermore, in mines, in which contamination of the working pit by the exhaust gas of the dump trucks causes a big problem, the trolley-assisted dump trucks are used in practice for decreasing the amount of the exhaust gas. More especially, cheap main electric supply collected by means of a pair of pantographs from two-line contact wires of overhead contact system is utilized for the full load up-hill course starting from the working pit located at bottom to outside of the mine and to the contrary, the vehicle engine is used for the no load down-hill returning course.
The present invention relates particularly to an offset detecting device of the pantographs for the trolley-assisted dump trucks for protecting pantographs mounted on such trolley-assisted dump trucks.
2. Related Art Statement
In the full load up-hill course, in which the trolley-assisted dump trucks run in trolley mode, as there are no rails provided in general like railway systems and hence the trolley-assisted dump trucks run along so called endless rails, offset or off-center accidents of pantographs from the overhead contact systems may often be happened whenever the trolley-assisted dump trucks come out of the designated lane width which may be caused by doze of driver or careless driving.
Some conventional examples of such an offset detecting device of pantographs are shown in FIGS. 1-a, 1-b, and 1-c, which operate as a pneumatic controlling device.
FIG. 1-a shows a perspective view of the portion of pantographs of such a trolley-assisted vehicle, FIG. 1-b is a more detailed view of one pantograph and FIG. 1-c shows a controlling circuit thereof.
In these figures, reference numeral 1 (1') designates contact wire of the overhead system, and 2 (2') shows pantograph structure having two collector sliding plates 2a and 2b arranged in parallel. Reference numeral 3 shows frame work of the pantograph, 4 an air cylinder, 5 and 6 are electromagnetic valves, 8 a mechanical valve attached on the pantograph collector device for detecting offset condition of the pantographs, 10 a check valve, 11 is a throat valve of air line, 12 is a vehicle mounted battery, and a terminal 100 shows a vehicle mounted controlling pressurized air intake. In the figure, a thick line shows the pneumatic lines and dotted line shows the route of electric signal.
Among the above figures, FIG. 1b shows mounting condition of the mechanical valve mounted at pantograph offset condition detecting position of the pantograph 2. In FIG. 1b, 2 generally shows the structure of the pantograph collector, 2a a collector sliding plate, 81 a pressing plate, 82 a restoring spring, 8 a body of the mechanical valve, 83 a pressing rod for operating the mechanical valve, and 84 is an air line. Normally, by the action of the restoring spring 82, the pressing plate 81 would not press the pressing rod 83. But if the detecting position of the contact wire of the overhead system 1 is reached, the pressing plate 81 is pressed down further by overcoming the counteracting bias pressure of the restoring spring 82 and it presses down the pressing rod 83. By this action, the mechanical valve 8 is operated to exhaust the pressurized air in the air line 84.
Referring to the control circuit shown in FIG. 1c, normally, the supply of pneumatic pressure to the air cylinder 4 or evacuation of the same therefrom is controlled by an electromagnetic valve 5 and the pantograph is raised or lowered. During the trolley mode running with the pantograph in the raised up working position, if the mechanical valve 8 for the detection of offset condition is operated and the pressurized air in the air line 84 is evacuated, a pressure switch 9 detects this pressure down condition. A check valve or a throttle valve 10 is to limit air flow amount fed from pressurized air intake 100. By the operation of the pressure switch 9, an electric signal from the battery 12 energizes the electromagnetic valve 5 to lower down the pantograph. At the same time it energizes an electromagnetic valve 6 to operate a quick exhaust valve 7 to immediate evacuate of the air in the air cylinder 4 to lower the pantograph down to prepare the emergency condition. The check valve 10 is provided to prevent operation of the quick exhaust valve 7 in a normal pantograph lowering operation.
In the abovementioned conventional system, there is no much trouble concerning the electric insulation of the high voltage electric supply of the contact wire of the overhead system. However, there is a disadvantage in that the response speed of the mechanical valve is slow. Namely, the time required between the start of depressing the pressing plate 81 by the contact wire 1 of the overhead system and the operation of the mechanical valve 8 to bringing down the pantograph is too long. Thus the pantograph may collide against suspension member of the overhead systems during the above relatively long term and hence the safety protection for the pantograph is insufficient.